Wide-field microwave magnetic field imaging with nitrogen-vacancy centers in diamond

TL;DR

This paper introduces a wide-field NV center-based magnetometry method for non-invasive imaging of weak microwave magnetic fields with high spatial resolution, sensitivity, and a large field of view, using a differential measurement protocol.

Contribution

It presents a novel differential Rabi frequency measurement protocol enabling wide-field imaging of microwave magnetic fields with NV centers, extending capabilities to weak field detection.

Findings

Achieved 9 μT/Hz^{1/2} sensitivity for 2.57 GHz MW fields

Covered a 340×340 μm^2 field of view with μm-scale resolution

Demonstrated detection of weak MW fields difficult to measure with standard methods

Abstract

Non-invasive imaging of microwave (MW) magnetic fields with microscale lateral resolution is pivotal for various applications, such as MW technologies and integrated circuit failure analysis. Diamond nitrogen-vacancy (NV) center magnetometry has emerged as an ideal tool, offering $\mu$m-scale resolution, millimeter-scale field of view, high sensitivity, and non-invasive imaging compatible with diverse samples. However, up until now, it has been predominantly used for imaging of static or low-frequency magnetic fields or, concerning MW field imaging, to directly characterize the same microwave device used to drive the NV spin transitions. In this work we leverage an NV center ensemble in diamond for wide-field imaging of MW magnetic fields generated by a test device employing a differential measurement protocol. The microscope is equipped with a MW loop to induce Rabi oscillations between NV spin states, and the MW field from the device-under-test is measured through local deviations in the Rabi frequency. This differential protocol yields magnetic field maps of a 2.57 GHz MW field with a sensitivity of $\sim$ 9 $\mu$T Hz$^{-1/2}$ for a total measurement duration of $T = 357$ s, covering a $340\times340$ $\mu$m$^2$ field of view with a $\mu$m-scale spatial resolution and a DUT input power dynamic range of 30 dB. This work demonstrates a novel NV magnetometry protocol, based on differential Rabi frequency measurement, that extends NV wide-field imaging capabilities to imaging of weak MW magnetic fields that would be difficult to measure directly through standard NV Rabi magnetometry.